Miles Blair Cody Dinges Greg Entzel Derek Glass THE BLUE BOX -
CDR
Slide 2
PROJECT UPDATE Class A Amplifier Analog Board Update: Thorough
understanding of tube theory and single-ended design 30W design not
economically feasible with single ended design Currently driving
10W using 250VDC Plan to drive closer to 15W signal power. Foot
Pedal & Effects Circuitry Digital & Analog Board I/O Larger
SPI potentiometers set with good accuracy at 8-bit precision Plan
to implement effects/preset command signals using digital logic
MSP430 Digital Board Update: SPI drivers set potentiometers with
ease Plan to transition to I 2 C with surface mount potentiometers
Plan to focus on interfaces, buffers, and database before UI
Slide 3
FUNCTIONAL DECOMPOSITION LEVEL 0
Slide 4
FUNCTIONAL DECOMPOSITION LEVEL 1
Slide 5
FOOT PEDAL LEVEL 2 Foot Button Inputs: User button press
Outputs: Logic message to the processor Implementation: Digital
Button integrated circuit triggers message Test Plan: Power the
integrated circuit and press the button while using an oscilloscope
to check that an I2C message was generated. Preset number display
Inputs: I2C with new preset number sent from the processor.
Outputs: 7 segment display to user Implementation: Premade
integrated circuit with display Test Plan: Send a I2C and observe a
display change.
Slide 6
SMARTPHONE LEVEL 2 Phone computer system Inputs: User interface
input Outputs: Wireless messages to the phone Bluetooth modem
Implementation: Android operating system with application software
Test Plan: Unit tests for individual software modules. Phone
Bluetooth modem Inputs: Inbound wireless messages from the device
Bluetooth modem Outputs: Outbound wireless messages to the device
Bluetooth modem Implementation: Android device and operating system
Test Plan: It is built into the phone, hope it works.
Slide 7
DIGITAL BOARD LEVEL 2 Device Bluetooth modem Inputs: Inbound
messages Outputs: Outbound messages Implementation: Premade device
with software Test Plan: Send a message and read the TX pin with an
oscilloscope. Processor Inputs: Button hit messages and inbound
Bluetooth messages Outputs: Foot pedal display changes, outbound
Bluetooth messages, and I2C messages for effects changes, EQ
changes, volume changes, and effect bypass switch changes
Implementation: Premade hardware and custom software Test Plan: Use
the phone and foot pedal to change the preset or change an effect
setting and observe outgoing I2C messages to the digital
potentiometers and seven segment display.
Slide 8
MSP430G2553 MICROCONTROLLER Inexpensive UART connection to
Bluetooth modem I2C drivers for digital potentiometers and effect
bypass switches 20 pin designs offer enough general purpose pins
for the foot-pedal buttons 16 kB non-volatile flash memory to store
presets and performance sets
Slide 9
DIGITAL POTENTIOMETERS AND SWITCHES Digital potentiometers have
256 resistance settings Control Analog effects circuits and
amplifier Digital Switches bypass effects that are not used in
active preset Can all be connected to the same I2C serial bus
Bluesmirf RN-42 Bluetooth Modem Class 2 Bluetooth Device 18 meter
range makes it perfect for a stage
Slide 10
DIGITAL BOARD SYSTEM CONTEXT DIAGRAM
Slide 11
ANALOG BOARD LEVEL 2
Slide 12
Analog effects circuits Inputs: Guitar signals from electric
guitar and I2C messages containing digital potentiometer changes
and relay changes to bypass/connect effect circuits Outputs: Analog
signal to the equalizer circuit. Implementation: These will be a
series of filters and analog effects circuits. The effects can be
adjusted by digital potentiometers, and they are selected
on/bypassed by a digital relay integrated circuit that is
controlled by the processor using I2C messages. Test Plan: Input a
signal generator signal 100 mV peak to peak and use an oscilloscope
to observe an alteration in the input signals wavform. EQ filter
Inputs: Analog signal from the effects circuits and I2C messages
with potentiometer changes for the filters in the equalizer.
Outputs: Analog signal to the power amplifier. Implementation:
Series of bandpass/highpass/lowpass filters that are adjusted with
digital with digital potentiometers. Test Plan: Input a sinusoidal
waveform signal 200 mV peak to peak and use an oscilloscope to
observe an alteration in the input signals amplitude for different
frequencies. Analog amplifier Inputs: The altered analog signal
from the equalizer. Outputs: Amplified analog signal to drive the
speaker. Implementation: High power tubes to amplify the signal in
2 stages and an audio transformer steps down the voltage to a level
where the current is high enough to drive the speaker. Test Plan:
Input a 100 mV signal from a waveform generator and observe 15W
signal from the power amplification stage. Then connect the speaker
and check that it sounds correct. Speaker Inputs: Amplified analog
signal from the amplifier Outputs: Sound Implementation: Premade
inductive driver Test Plan: Connect to amplifier and hear if it
sounds correct.
Slide 13
SINGLE-ENDED AMPLIFIER SCHEMATIC Pre-Amplifier (Twin Triode
12AX7): 45 X 45 = 2025 Gain Power Amplifier (Power Beam Pentode
6L6GC): 10W Signal Output
Slide 14
PRE-AMP DESIGN Triode (12AX7): Anode/Plate: Determines
operating point of tube. Delivers output signal of gain stage
Cathode: Determines sensitivity to input. Grid: Input signal.
Heater: Improve cathode conductivity. Minimize effects of any
gas.
Slide 15
PRE-AMP DATA SHEET CONSIDERATION
Slide 16
V SUPPLY =250V V PLATE =175V V IN,MAX =100mV V CATHODE =1V I
TRIODE =1.65mA V R_P =75V R P =V R_P / I TRIODE 46 Kohm Plate
Resistor R K =V CAT. / I TRIODE 610 Ohm Cathode Resistor
Slide 17
Mutual Conductance: g m = 1.950 mA/VPlate Resistance: r p = 53
KOhm
Slide 18
PREAMP EQUIVALENT CIRCUIT r P = 53 Kohm R P = 51 Kohm R LOAD =
200 Kohm R K = 680 Ohm R TOT = r p || R P || R LOAD = 23 KOhm g m =
1.950 mA / V V IN,MAX = 100 mV i P = g m * V IN,MAX =.195 mA V OUT
= R TOT * i P A V = V OUT / V IN,MAX = 45
Slide 19
PRE-AMP SIMULATION RESULTS V PP = 7.6V V P = 3.8V A V = 38
Slide 20
PRE-AMP TEST RESULTS V PP = 8.6V V P = 4.3V A V = 43
Slide 21
PRE-AMP GAIN / DISTORTION RESULTS First gain stage outputs 4.5V
peak. Second gain stage biased to 1.5V Input signals near and above
1.5V P cause distortion Begins at 90V PP Set currently by a 500
Kohm logarithmic potentiometer
Slide 22
POWER OUTPUT TUBE Power Beam Tetrode: (6L6GC) Anode, Cathode,
Heater, Control Grid: Same roles as triode, except plate drives an
inductive load. Suppressor Grid: Help increase output current.
Reduce effect of oscillations Tied to ground to reduce control
grid-ground capacitance internally Screen Grid: Similar function to
suppressor, close to high voltage.
Slide 23
OUTPUT DESIGN STARTING PLACE Output transformer (125ESE) rated
for a bias of 80mA before saturation and frequency attenuation Some
saturation emulates compression and works well with high tube gain
Bias for 75 mA
Slide 24
CRITICAL OUTPUT DESIGN
Slide 25
POWER OUTPUT Transformer Input Waveform Speaker Waveform 17.5V
PP indicates near 5W output V RMS = 6.189 P = V RMS 2 / R P = 4.8W
388 V P ! A lot of energy stored in the output transformer
Slide 26
NOTE ON POWER OUTPUT There is no standard for determining
ratings for amplifiers 5W was only obtained at 100Hz and 100mV p
Used a guitar with humbucker pickups (generate a 200mV P signal)
Drove the speaker to V PP = 23 V (a 10W output) without noticeable
distortion Drove the speaker to V PP,MAX = 35 V (near 20W output)
with noticeable distortion Safe to rate the amplifier at 8-10W as a
maximum recommended playing volume This rating is somewhat flexible
due to tone desirability from overdriving pentode This power output
is expected as it is biased near 20W with an expected 50%
efficiency in a single ended setup
Slide 27
PLAYING DEMONSTRATION Note lack of hum: Quality DC voltages,
requires high-fidelity supply design Note frequency response:
Special consideration given to sizing biasing and coupling
capacitor Special consideration given to audio transformer
saturation current Note the gain/distortion: Smooth gain, subtle
yet full. Additional overdrive will square out signal more
dramatically Lacking Tone Design: Equalizer will improve audio
quality. Capacitors may need to be decreased to reduce signal drift
and popping
Slide 28
PRELIMINARY PARTS LIST PartCost 12AX7 Ruby$12.57 6L6GC$17.50 5
x 100uF 330V caps$6.00 3x4.7K, 2x200K, 2x51K, 680, 910, 200, 510
Resistors$10.00 500K & 1M Logarithmic Potentiometer$3.00 Power
Transformer 269AX$45.00 Output Transformer 125ESE$70.00 Wood &
Screws$50.00 400W Peavey Scheffield$30.00 Android Droid$50.00 20 x
I 2 C Potentiometers$25.00 I 2 C Switches$10.00 Effects Components
(R,L,C, Op-amps)$150.00 Amplifier PCB$33.00 Effects PCB$33.00
MSP420 Dev. Kit$3.50 Approximate Total: $548.57
Slide 29
UPDATED SCHEDULE - HARDWARE
Slide 30
UPDATED SCHEDULE - SOFTWARE
Slide 31
DIVISION OF LABOR TaskDerek GlassCody DingesGreg EntzelMiles
Blair Build and test filtersX X Build power supplyXX X Build
amplifierXXXX Android initialization XX Design User InterfaceXXXX
MSP430 data Interfacing XX Foot Pedal Interfacing XX Construction
of AmpX X Altium DesignXX
Slide 32
CURRENT HIGH RISK FACTORS Hardware: Power Supply Stability
Software: I 2 C Address Space UART Capability of MSP430 vs. ARM M0
Flash Memory Capacity